Cassette half having multi-layer molded construction

ABSTRACT

A tape cassette includes a pair of cassette halves and a pair of hubs enclosed between the cassette halves, and about which a recording medium, or tape can be wound. Each cassette half includes a first molded body and a second molded body overlying it. The first molded body has a first principal surface and a first upstanding wall which is perpendicular to the principal surface and forms an integral part thereof and a part of a peripheral surface of the half. The second molded body has a second principal surface which is generally rectangular and overlies the first principal surface, and a second upstanding wall connected to the first upstanding wall to form the peripheral surface of the half therewith, forming an integral part of the second principal surface and surrounding it. The first and second upstanding walls are connected by a junction having a thickness increasing gradually across the thickness of the half.

This application is a division of application Ser. No. 08/275,364 filedJul. 15, 1994, now U.S. Pat. No. 5,508,870.

BACKGROUND

1. Field of the Invention

The present invention relates to a cassette half and a tape cassette.More particularly, the present invention relates to a cassette halfhaving a two-layer structure and a tape cassette formed by a pair ofsuch cassette halves.

2. Background of the Invention

There is known a cassette for e.g. a sound recording and reproducingtape which includes a pair of cassette halves fitted together, and apair of reel hubs which are enclosed between the cassette halves, and onwhich the tape can be wound. Each cassette half may have a two-layerstructure as shown at 101 in FIG. 1, and include an inner resin layer102 formed from a resin having a low modulus of elasticity, and an outerresin layer 103 formed from a resin having a high modulus of elasticityon the inner resin layer 102, as shown in FIGS. 1 to 3. The inner resinlayer 102 improves the vibration-damping property of the cassette half.

The cassette half 101 is formed by injection molding the inner resinlayer 102 in a mold, and the outer resin layer 103 on the outer surfaceof the inner resin layer 102. The outer resin layer 103 has a thinportion 104 lying on the inner resin layer 102, and a thick portion 105contiguous to the thin portion 104, both as viewed across the thicknessof the cassette half.

Each cassette half 101 has in the principal surface a pair of holes 107through which the reel shafts, respectively, of a tape recording and/orreproducing apparatus can be inserted, as shown in FIG. 1. The twocassette halves 101 are joined together by screws, etc. to assemble atape cassette 111, as shown in FIG. 1. Each cassette half 101 has in oneof its edge surfaces a plurality of cuts which enable the cassette 111to have a plurality of openings 108 through which the tape can be partlyexposed, and into which the heads, pinch rollers, etc. of the recordingand/or reproducing apparatus can be inserted. Reel hubs 109 and 110partly project into the holes 107, respectively, and are rotatable bythe reel shafts passed through the holes 107.

The outer resin layer 103 of each cassette half 101 has, however, anabrupt change in thickness between its thin and thick portions 104 and105, as FIG. 2 shows that the thick portion 105 has an end surface 106which is substantially perpendicular to the thin portion 104, or has anangle of about 90° thereto. The shape of the outer resin layer 103 asdescribed is apparently responsible for the problems which will bepointed out below:

(1) When the outer resin layer 103 hardens after injection molding, itsshrinkage occurs to a greatly different degree between its thin andthick portions 104 and 105. The thick portion 105 undergoes much moreshrinkage than the thin portion 104. As a result, the thick portion 105becomes warped, as shown in FIG. 3, and the cassette half 101 is,therefore, deformed;

(2) The use of any cassette half 101 deformed by the warpage of itsthick portion 105 has an adverse effect on the accuracy in thickness ofthe tape cassette 111; and

(3) The cassette 111 has a gap δ formed between the thick portions 105of the cassette halves 101, as shown in FIG. 3. The gap δ isundesirable, since it is likely that dust, or the like may enter thecassette through the gap, or that a magnetic tape 112 may be caught inthe gap, and thereby damaged.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide a cassette halfwhich can overcome the problems as hereinabove pointed out.

It is another object of this invention to provide a tape cassette whichcan overcome the problems as hereinabove pointed out.

According to one aspect of this invention, there is provided a cassettehalf including an inner resin layer and an outer resin layer formed byinjection molding and overlying the inner resin layer, the outer resinlayer having a thin portion overlying the inner resin layer and a thickportion adjoining the thin portion, the outer resin layer having betweenits thin and thick portions a boundary portion having a thicknessincreasing gradually from the thin to the thick portion.

According to another aspect of this invention, there is provided acassette half including a first molded body and a second molded bodyoverlying the first molded body, the first molded body having a firstprincipal surface and a first upstanding wall which is perpendicular tothe principal surface and forms an integral part thereof and a part of aperipheral surface of the half, the second molded body having a secondprincipal surface which is generally rectangular and overlies the firstprincipal surface, and a second upstanding wall connected to the firstupstanding wall to form the peripheral surface of the half with thefirst upstanding wall, forming an integral part of the second principalsurface and surrounding it, the first and second upstanding walls beingconnected by a connecting portion having a thickness increasinggradually across the thickness of the half.

According to still another aspect of this invention, there is provided atape cassette including a pair of cassette halves and a pair of hubswhich are enclosed between the halves, and about which a recordingmedium in tape form can be wound, each cassette half including a firstmolded body and a second molded body overlying the first molded body,the first molded body having a first principal surface and a firstupstanding wall which is perpendicular to the principal surface andforms an integral part thereof and a part of a peripheral surface of thehalf, the second molded body having a second principal surface which isgenerally rectangular and overlies the first principal surface, and asecond upstanding wall connected to the first upstanding wall to formthe peripheral surface of the half with the first upstanding wall,forming an integral part of the second principal surface and surroundingit, the first and second upstanding walls being connected by aconnecting portion having a thickness increasing gradually across thethickness of the half.

According to a still different aspect of this invention, there isprovided a cassette half including a first molded body and a secondmolded body overlying the first molded body, the first molded bodydefining a first principal surface having anti-peeling means, the secondmolded body defining a second principal surface which is generallyrectangular and overlies the first principal surface, and an upstandingwall forming an integral part of the second principal surface andsurrounding it, the anti-peeling means being defined by a plurality ofdiscrete concavities so arranged as to form the boundary of an areaincluding portions corresponding to the gates of a mold for the firstmolded body.

According to a still different aspect of this invention, there isprovided a tape cassette including a pair of cassette halves, a pair ofhubs which are rotatably supported between the halves, and about which arecording medium in tape form can be wound, and a sheet memberinterposed between the inner surfaces of the halves and each hub andhaving portions contacting the hub, each cassette half including a firstmolded body and a second molded body overlying the first molded body,the first molded body defining a first principal surface havinganti-peeling means, the second molded body defining a second principalsurface which is generally rectangular and overlies the first principalsurface, and an upstanding wall forming an integral part of the secondprincipal surface and surrounding it, the first principal surfaceincluding a smooth surface on which the hubs are rotatably supported.

As the first and second molded bodies forming the cassette half of thisinvention are connected by a junction having a thickness increasinggradually across the thickness of the cassette half, the second moldedbody overlying the first molded body is not warped, or otherwisedeformed. Therefore, the tape cassette of this invention is not deformedto form any undesirable gap between its halves.

The second molded body is of improved quality, since the resin flowssmoothly from the inner region defined by the concavities to the outerregion when the first molded body is molded.

As the principal surface of the first molded body includes a smoothsurface on which the hubs are rotatably supported, it is possible tolower the contact resistance between that surface and the sheet memberscontacting the inner surface of the cassette halves, and thereby preventthe formation of ground dust by the sheet members during the rotation ofthe hubs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly cutaway perspective view of a tape cassette of thetype to which this invention pertains;

FIG. 2 is an enlarged view of a part of the tape cassette shown in FIG.1;

FIG. 3 is a view showing the drawback of the tape cassette shown in FIG.1;

FIG. 4 is an exploded perspective view, as taken from top and front, ofa cassette half and a guide block in a tape cassette according to afirst embodiment of this invention;

FIG. 5 is an enlarged perspective view, as taken from top and back, of apart of the cassette half and the guide block in the tape cassetteaccording to the first embodiment of this invention;

FIG. 6A is a partly cutway perspective view of the tape cassetteaccording to the first embodiment of this invention;

FIG. 6B is a rear elevational view thereof;

FIG. 7A is a top plan view of the lower half of the tape cassetteaccording to the first embodiment of this invention;

FIG. 7B is a sectional view taken along the line B--B of FIG. 7A;

FIG. 7C is a sectional view taken along the line C--C of FIG. 7A;

FIG. 8 is a sectional view showing the shape of a concavity formed inthe half of the tape cassette according to the first embodiment of thisinvention;

FIG. 9 is an elevational view explaining the positioning of the guideblock in the tape cassette according to the first embodiment of thisinvention;

FIG. 10 is a partly cutaway perspective view of a tape cassetteaccording to a second embodiment of this invention; and

FIG. 11 is an enlarged view of a part of the tape cassette shown in FIG.10.

DESCRIPTION OF THE INVENTION

The cassette half and tape cassette of this invention will now bedescribed in detail with reference to the drawings. Reference is firstmade to FIGS. 4 to 9 showing the tape cassette according to the firstembodiment of this invention. FIG. 4 shows the lower half 31a of theaudio tape cassette and a guide block 55.

The lower half 31a is a product of the so-called "double-shot molding"including a first molded body 32 and a second molded body 33 overlyingeach other, and is, as a whole, shaped like a box having an open top. Itcan be made by, for example, injection molding. The first molded body 32is first molded, and held in a mold, and the molding material is, then,injected into the mold to mold the second molded body 33 over the firstmolded body 32. The upper half 31b of the cassette is basically of thesame construction with the lower half 31a, and no detailed descriptionthereof will, therefore, be made.

The first molded body 32 is formed from a synthetic resin having a lowmodulus of elasticity, such as nylon, polypropylyne or polyurethane, andhas a wall thickness of about 0.6 mm.

The first molded body 32 is provided at its two front corners with tworeinforcing ribs 34, and 35 which project upwardly from its principalsurface 32a and which are spaced apart from each other along the lengthof the cassette half, as shown in FIGS. 4, 7A and 7C. The first moldedbody 32 is also provided in its central portion with two circular holes36 and 37 spaced apart from each other along the length of the cassettehalf and two hub positioning ribs 38 and 39 extending along the inneredges of the holes 36 and 37, respectively. The first molded body 32also has a rectangular opening P between the holes 36 and 37.

The first molded body 32 has also a plurality of discrete concavities 41so arranged as to define the area including portions corresponding to apair of gates 40 in a mold not shown and the area to be finally filledwith the resin. The portion lying between every two adjoiningconcavities 41 is preferably located on a line connecting the portionscorresponding to the gates 40 and the area to be finally filled with theresin.

The principal surface 32a of the first molded body 32 includes finelyroughened or satinized surfaces M having a roughness of 10 microns RZexcept in the vicinity of each concavity 41 and each of the ribs 38 and39, and other protrusions formed by the concavities not shown of themold not shown, as shown in FIGS. 4, 7A and 7B. The principal surface32a also includes a smooth surface N in its portions supporting reelhubs 3 and 4 and facing the hub contacting portions of sheet members yetto be described, as shown in FIGS. 4, 7A and 7C.

Each concavity 41 is a combination of a first concavity 41a open in theprincipal surface 32a and having a rectangular cross section, and asmaller second concavity 41b formed like a dovetail groove in the bottomof the first concavity 41a, as shown in FIG. 8.

Recesses 32b are formed in the middle of the rear edge of the firstmolded body 32, and form a part of openings provided at the rear edge ofthe cassette half for enabling the detection of the type of a magneticrecording medium 5 in tape form.

The second molded body 33, which partly covers the opening P, is formedfrom a synthetic resin composition having a high modulus of elasticity,such as a mixture of nylon and an inorganic substance such as zinc oxideor aluminum silicate, and has a wall thickness of about 1.2 mm.

The second molded body 33 is provided near its front corners with a pairof shafts 42 and 43 supporting a pair of guide rollers 12 and 13rotatably, and a pair of guide pins 44 and 45 positioned near the guiderollers 12 and 13, respectively, as shown in FIGS. 4 and 6A. The guiderollers 12 and 13 are positioned close to the opposite ends,respectively, of the guide block and are rotatably supported by theshafts 42 and 43, respectively, for guiding the recording medium 5. Eachof the shafts and guide pins forms an integral part of the second moldedbody 33.

The second molded body 33 is provided in the mid-portion of its frontedge with a trapezoidal outward protrusion 46 having a second surface46a which is lower than a first surface 33a having the guide pins 44 and45. An upwardly or inwardly projecting boss 47 for positioning the guideblock forms an integral part of the second surface 46a in themid-portion of its rear edge.

The first and second surfaces 33a and 46a define a stepped surface 48therebetween near each of the two front corners of the second moldedbody 33. Each stepped surface 48 has at its rear end a projection 49forming an integral part of the second molded body 33 and defining apair of surfaces 49a and 49b for positioning the guide block downwardlyand in the direction of insertion of the cassette, or head,respectively. The second surface 46a is provided with a pair of pins 50spaced apart from each other along the length of the cassette half forpositioning the guide blocking the direction of removal of the cassette.

The second molded body 33 is also provided along its front edge with twopairs of holes 51 and 52 opening outwardly and inwardly of theprotrusion 46 and providing passages for the capstan and guide pin, notshown, of a tape recorder not shown. The second molded body 33 has awindow 54 provided in the center of the cassette half for enabling thevisual inspection of the inside of the cassette. The window 54 faces theopening P, extends along the length of the cassette half, and is closedby a transparent member 53 secured to the cassette half by a pluralityof pins projecting from the second molded body 33 along the window 54and deformed by heat.

The guide block 55 for guiding the travel of the recording medium ispositioned along the front edge of the lower cassette half 31a andpartly overlies the protrusion 46, as is obvious from FIG. 5. The guideblock 55 has a pair of curved guide surfaces 55a and 55b extending fromits opposite ends, respectively, to a central protrusion 55c along itsback facing the reel hubs, and a pair of reinforcing ribs 56 and 57extending along the lower edges of the guide surfaces 55a and 55b,respectively. The central protrusion 55c has a hole 58 through which theboss 47 is passed.

The guide block 55 is provided at each end with a bearing lug 59 havinga mounting surface 59a adapted to rest on one of the stepped surfaces 48on the cassette half. Each lug 59 has a recess 60 defining twopositioning surfaces 60a and 60b adapted to engage the positioningsurfaces 49a and 49b, respectively, adjacent to one of the steppedsurfaces 48. Each lug 59 is also provided above the recess 60 withanother recess 61 defining two positioning surfaces 61a and 61b adaptedto engage two positioning surfaces formed on the upper cassette half notshown near each front corner thereof, and similar to the positioningsurfaces 49a and 49b on the lower cassette half. The recess 61 has adepth h₂ which is smaller than the depth h₁ of the recess 60, as shownin FIG. 9. The guide block 55 has also two pairs of recesses 62a and62b. One pair of recesses 62a are provided at the bottom of the guideblock 55, and spaced apart from each other for receiving the pins 50 onthe lower cassette half 31a, while the other pair of recesses 62b areprovided at the top of the guide block 55 and above the recesses 62a,respectively, for receiving the pins 50 not shown on the upper cassettehalf 31b.

The upper and lower cassette halves 31b and 31a are joined together withe.g. screws to assemble the cassette, as shown in FIG. 6A. A pair ofreel hubs 3 and 4 and a pair of sheet members 6 and 7 are enclosedbetween the cassette halves 31a and 31b. The reel hubs 3 and 4 engagethe ribs 38 and 39, respectively, and are rotatable by the reel shaftsof a tape recorder which are inserted through the holes 36 and 37, sothat the magnetic recording medium, or tape 5 may be wound on the reelhub 3 or 4.

The sheet members 6 and 7 interposed between the reel hubs 3 and 4 andthe inner surfaces of the cassette halves 31a and 31b, respectively, sothat the reel hubs 3 and 4 may be sandwiched between the sheet members 6and 7, and so that any frictional resistance to the rotation of the reelhubs may be reduced. Each sheet member 6 or 7 has at least a surfaceformed from a transparent material of low frictional resistance. Eachsheet member 6 or 7 has a pair of parallel portions 6a or 7a extendingalong the length of the cassette and contacting the reel hubs 3 and 4.Each hub contacting portion 6a or 7a is a ridge projecting toward thereel hubs 3 and 4. Each sheet member 6 or 7 also has a pair of openingsin which the ribs 38 and 39 are fitted, though they are not shown.

The magnetic recording medium, or tape 5 travels from one of the reelhub 3 to the other reel hub 4 past the guide roller 12, the lugs 59 onthe guide block 55 and the guide roller 13. The tape 5 traveling pastone of the lugs 59 is exposed through a plurality of openings 65 alongthe front edge of the cassette. If the cassette is placed in a taperecorder, the reel shafts of the recorder pass through the holes 36 and37, and the capstan and guide pins through the holes 51 and 52. If thetape recorder is set for operation in the recording or reproductionmode, its magnetic head, pinch rollers, etc. project into the cassettethrough the openings 65. As a result, the tape 5 travels from one of thereel hubs 3 or 4 to the other, so that the recording of an informationsignal on the tape 5 or its reading from the tape 5 may be effected bythe magnetic head.

The first and second molded bodies 32 and 33 forming each cassette half31a or 31b have a boundary, or junction 30 so shaped as to give thesecond molded body 33 a gradually increasing thickness from its thinwall portion 33b to its thick wall portion 33c, as shown in FIG. 6B.More specifically, the junction 30 is arcuately shaped. The junction 30so shaped ensures that the resin forming the second molded body 33shrink only to a gradually increasing degree in the direction of thearrow in FIG. 6B when it hardens, and that no undesirably greatdifference in shrinkage occur between the thin and thick wall portions33b and 33c. Therefore, the second molded body 33 is not warped, and nocassette half 31a or 31b is warped, or otherwise deformed.

The first molded body 32 in each cassette half as hereinabove describedhas between every two adjoining concavities 41 a thickness which isgreater than its thickness below each concavity 41. The resin passage inthe mold not shown maintains an equal size along its depth in itsportion designed to form the first molded body 32 between every twoadjoining concavities 41, so that the resin injected to form the firstmolded body 32 may smoothly flow from the inner region defined by theconcavities 41 to the outer region. As the resin passage in the molddoes not have to be enlarged in its portion for forming any concavity inthe first molded body 32, it is unlikely that any projection, not shown,on the first molded body 32 may be melted in the second molded body 33when the latter is injection-molded.

It is possible to achieve the necessary contact resistance between thefirst molded body 32 and the mold not shown when the mold is opened, ifthe mold has an appropriately roughened surface. Although no finelyroughened surface is made in the vicinity of any of the reinforcing ribs34 and 35, hub positioning ribs 38 and 39, and other projections formedby the concavities not shown of the mod as is obvious from FIG. 7A, itis possible to achieve the necessary contact resistance as a result ofthe shrinkage of the resin upon cooling, as the areas M between thoseprojections and the concavities of the mold are finely roughened.

The principal surface 32a of the first molded body 32 includes a smoothsurface formed by the appropriately finished surface of the mold forlowering any contact resistance between its portions around the reelhubs 3 and 4 and its portions contacting the sheet members 6 and 7. Theprincipal surface 32a also includes a smooth surface which lowers thecontact resistance between the hub contacting portions 6a and 7a of thesheet members 6 and 7 and the principal surface 32a.

The depth h₁ of the recesses 60 of the guide block 55 is greater thanthe depth h₂ of the recesses 61 as shown in FIG. 9, so that a gap may beformed between the lower cassette half 31a and the guide block 55 if theguide block 55 is positioned upside down. The gap can be visuallyrecognized to teach that the guide block 55 is wrongly positioned.

The positioning surfaces 49b of the protrusions 49 on the lower cassettehalf 31a ensure the accurate horizontal positioning of the guide block55 on the lower cassette half 31a. The provision of similar positioningsurfaces on the upper cassette half 31b ensures the accurate horizontalpositioning of the guide block 55 to a further extent.

Although the surface M has been described as having a roughness of 10microns RZ, it is merely illustrative, and may range from 5 to 30microns RZ.

Although the ribs 56 and 57 have been shown as being formed along thebottom of the guide block 55, they may alternatively be formed along itstop, if the recesses 61 are formed with a depth which is greater thanthat of the recesses 60.

Reference is now made to FIGS. 10 and 11 showing a tape cassetteaccording to a second embodiment of this invention. The tape cassette 71has a pair of halves 72 and 73. Each cassette half 72 or 73 is two-layerstructure including an inner resin layer 74 as a first molded body andan outer resin layer 75 formed as a second molded body and overlying theinner resin layer 74. The inner resin layer 74 is of a relatively softsynthetic resin having a low modules of elasticity, such as nylon,polypropylene or polyurethane. The outer resin layer 75 is of arelatively hard synthetic resin composition having a high modules ofelasticity, such as a mixture of nylon and an inorganic substance suchas zinc oxide or aluminum silicate. Thus, the inner resin layer 74serves for damping vibration, while the outer resin layer 75 gives thenecessary rigidity to the cassette half 72 or 73.

The outer resin layer 75 of each cassette half includes a thin or narrowportion 76 overlying the inner resin layer 74 and a thick or broadportion 77 connected to the thin portion 76. The thin or thick portion76 or 77 is thin or thick as viewed across the thickness of the cassette71, as is obvious from the FIG. 10 or 11. The thin and thick portions 76and 77 are connected by a junction or boundary portion 78 having athickness or width increasing gradually from the thin portion 76 to thethick portion 77. The junction 78 has a surface inclined at an angle of45° between the thin and thick portions 76 and 77, as is obvious fromFIG. 11. Thus, the junction 78 gradually increases its thickness orwidth from the thin portion 76 to the thick portion 77.

The cassette 71 has an opening 81 formed between its halves 72 and 73for the insertion of a magnetic head, a pair of openings 82 and 83formed on the opposite side of the opening 81 from each other for theinsertion of pinch rollers, and a pair of holes 84 and 85 formed throughthe top and bottom surface of its halves 72 and 73 for the insertion ofspindles.

When the resin injected to mold the outer resin layer 75 of eachcassette half is cooled, it shrinks to a gradually increasing extentfrom the thin portion 76 to the thick portion 77. Any abrupt change doesnot occur in the degree of shrinkage between the thin and thick portions76 and 77 that may cause the warpage of the outer resin layer 75 in anyway as shown in FIG. 3.

Although the angle as defined by the junction 78 has been stated as 45°,it can be increased to prolong the junction 78 to ensure to a furtherextent that the outer resin layer 75 be protected against warpage.

The tape cassette 71 is otherwise of the same construction with cassetteas hereinbefore described with reference to FIGS. 4 to 9. No repeateddescription of their common features is, therefore, made.

While the invention has been described in its preferred forms of audiotape cassettes, it is equally applicable to other types of tapecassettes.

What is claimed is:
 1. A cassette half comprising:a first molded bodyhaving a first principal surface and a first upstanding wall which issubstantially perpendicular to said first principal surface, said firstupstanding wall forming an integral part of said first principal surfaceand a part of a peripheral surface of said half; a second molded bodyoverlying said first molded body, said second molded body having asecond principal surface which overlies said first principal surface,said second molded body having a second upstanding wall which isessentially perpendicular to said second principal surface, said secondupstanding wall forming an integral part of said second principalsurface and surrounding said second principal surface, said secondupstanding wall forming part of the peripheral surface of said half,said second upstanding wall connecting with said first upstanding wallto form a complete peripheral surface of said half, said first andsecond upstanding walls being connected over a junction area so that, ina plane defined by a surface of said upstanding walls, the respectivethickness of the first upstanding wall and the thickness of the secondupstanding wall gradually vary in a manner wherein a sum of thethicknesses of said first and second upstanding walls, as measured insaid plane, remains constant and equal to the thickness of said cassettehalf over said junction area.
 2. A cassette half according to claim 1,wherein a line defined by the connection between the first upstandingwall and the second upstanding wall, where the thickness of the firstupstanding wall and the thickness of the second upstanding wallgradually change, has an arcuately curved shape.
 3. A cassette halfaccording to claim 2, wherein a line defined by the connection betweenthe first upstanding wall and the second upstanding wall, where thethickness of the first upstanding wall and the thickness of the secondupstanding wall gradually change, is inclined with respect to thedirection in which the thicknesses of the first and second upstandingwalls are summed.
 4. A cassette half comprising:a first molded bodyhaving a first principal surface; a second molded body overlying saidfirst molded body, said second molded body having a second principalsurface which is generally rectangular and which overlies said firstprincipal surface, said second molded body having an integral upstandingwall which is essentially normal to said second principal surface, theupstanding wall being integral with said second molded body andsurrounding said second principal surface; and means for preventingseparation of said first molded body from said second molded bodyincluding a plurality of discrete concavities formed in said firstmolded body, said discrete concavities each having side walls which arearranged along lines forming the boundaries of an area includingportions of the first molded body corresponding to gates of a mold forthe material of said first molded body.
 5. A cassette half according toclaim 4, wherein each of said discrete cavities comprises a first cavityportion having a bottom wall and side walls interconnecting the bottomwall with said first principal surface and a second smaller cavityportion formed in the bottom wall of the first cavity, said secondsmaller cavity portion having a dovetail shaped cross-section in a planenormal to said first principal surface.